Auron was dead to begin with.. And Tidus was just a dream, and at that time the dream, Tidus, was fading away.. therefore he was dissapearing. And when he was in Zanarkand, I think that was a memory, I'm not quite sure, but I think it was. Hope this helps!

I was looking through these comments and most of these contradict each other. I'll try to explain.

1000 years ago, there was a war between the machina-machine- cities and Bevelle. Sin came and destroyed all the machina cities- including Zanarkand. The survivors from Zanarkand gave up their souls to become fayths-they are the aeons you summon- and their souls were set into stone. When they became fayths, they created a 'Dream Zanarkand' (NOT SIN... IT WAS THE FAYTHS) The 'Dream Zanarkand' was just like the real one when it still existed. 10 years ago: Somehow (they don't really explain) Jecht, Tidus' father, ended up in the 'real' world. A.k.a Spira. Jecht is imprison because people think he's crazy beside one person, Yuna's father, Lord Braska. Lord Braska asks Jecht to join him and Auron on his pilgrimage. Jecht agrees to go with. When they finally reach Zanarkand, they meet Lady Yunalesca, the first summoner to defeat Sin. She had defeated Sin by sacrificing her husband who became the Final Aeon. This is what Braska had to do. He had to choose someone he holds dear (he only has his guardians with him-Jecht and Auron) to turn into the Final Aeon. Jecht volunteers himself because he knows he will never be able to get back to his real home- 'Dream Zanarkand' Braska turns Jecht into the Final Aeon and everyone knows that when the summoner calls upon the Final Aeon, they end up dying. So Braska dies and Jecht defeats Sin. The Final Aeon is the exact same aeon that is Sin. The only difference is that the bad Sin is being controlled by Yu Yevon. When Jecht defeated the old Sin, Yu Yevon just transferred his soul into the Final Aeon which is Jecht. So basically Sin is 'reborn' Grieved that he lost two friends, Auron goes to Yunalesca and tries to kill her but ends up getting killed in the process. Jecht (I believe)-in Sin form- takes the now unsent Auron to 'Dream Zanarkand' to watch over Tidus. Sin is basically like the bridge between the two worlds (think avatar from The Last Airbender like how they are the bridge between the spirit world and the living world) Present time: Sin attacks Tidus' Zanarkand (Dream Zanarkand) and pulls him out into the real world. Not 1000 years into the future like they lead you to believe for most of the game. When the party finally defeats Sin: Auron disappears (was sent by Yuna) because he had fulfilled his task and was content enough to go to the Farplanes. Tidus disappears because he is part of the FAYTH'S dream and they kept dreaming because Sin was still alive. They had been tired of dreaming and wanted to rest which is why they needed Tidus to defeat Sin. So when Sin was defeated once and for all, the fayths could finally sleep for good therefor ending the 'Dream Zanarkand' and all that it had and was- including Tidus. Tidus was never real, he was only a dream.

I was looking through these comments and most of these contradict each other. I'll try to explain.

1000 years ago, there was a war between the machina-machine- cities and Bevelle. Sin came and destroyed all the machina cities- including Zanarkand. The survivors from Zanarkand gave up their souls to become fayths-they are the aeons you summon- and their souls were set into stone. When they became fayths, they created a 'Dream Zanarkand' (NOT SIN... IT WAS THE FAYTHS) The 'Dream Zanarkand' was just like the real one when it still existed. 10 years ago: Somehow (they don't really explain) Jecht, Tidus' father, ended up in the 'real' world. A.k.a Spira. Jecht is imprison because people think he's crazy beside one person, Yuna's father, Lord Braska. Lord Braska asks Jecht to join him and Auron on his pilgrimage. Jecht agrees to go with. When they finally reach Zanarkand, they meet Lady Yunalesca, the first summoner to defeat Sin. She had defeated Sin by sacrificing her husband who became the Final Aeon. This is what Braska had to do. He had to choose someone he holds dear (he only has his guardians with him-Jecht and Auron) to turn into the Final Aeon. Jecht volunteers himself because he knows he will never be able to get back to his real home- 'Dream Zanarkand' Braska turns Jecht into the Final Aeon and everyone knows that when the summoner calls upon the Final Aeon, they end up dying. So Braska dies and Jecht defeats Sin. The Final Aeon is the exact same aeon that is Sin. The only difference is that the bad Sin is being controlled by Yu Yevon. When Jecht defeated the old Sin, Yu Yevon just transferred his soul into the Final Aeon which is Jecht. So basically Sin is 'reborn' Grieved that he lost two friends, Auron goes to Yunalesca and tries to kill her but ends up getting killed in the process. Jecht (I believe)-in Sin form- takes the now unsent Auron to 'Dream Zanarkand' to watch over Tidus. Sin is basically like the bridge between the two worlds (think avatar from The Last Airbender like how they are the bridge between the spirit world and the living world) Present time: Sin attacks Tidus' Zanarkand (Dream Zanarkand) and pulls him out into the real world. Not 1000 years into the future like they lead you to believe for most of the game. When the party finally defeats Sin: Auron disappears (was sent by Yuna) because he had fulfilled his task and was content enough to go to the Farplanes. Tidus disappears because he is part of the FAYTH'S dream and they kept dreaming because Sin was still alive. They had been tired of dreaming and wanted to rest which is why they needed Tidus to defeat Sin. So when Sin was defeated once and for all, the fayths could finally sleep for good therefor ending the 'Dream Zanarkand' and all that it had and was- including Tidus. Tidus was never real, he was only a dream.

Damn. You've done your research. I guess I'll be the first to say Thank You for that summary of one huge game. Rly man, you're awesome!